I. Field of the Invention
This invention relates to methods and compositions for increasing the amounts of phosphorus and/or micronutrients available for uptake by plants from soils.
II. Description of the Prior Art
In order to maintain healthy growth, plants must extract a variety of elements from the soil in which they grow. These elements include phosphorus and the so-called micro-nutrients (e.g. copper, iron and zinc), but many soils are deficient in such elements or they contain them only in forms which cannot be readily taken up by plants (it is generally believed that essential elements cannot be readily taken up by plants unless they are present in dissolved form in the soil).
To counteract such deficiencies, sources of the deficient elements are commonly applied to soils in order to improve growth rates and yields obtained from crop plants. For example, phosphates are often added to soil to counteract a lack of phosphorus. Large deposits of rock phosphates are available in many locations, but untreated rock phosphates have low water (citric acid) solubilities, particularly in neutral or alkaline soil systems, and consequently do not provide an easily-assimilable source of phosphorus. In order to overcome this problem, rock phosphates are usually chemically converted to more soluble compounds (e.g. mono-ammonium phosphate or triple-super-phosphate) in large-scale fertilizer-manufacturing facilities. However, such conversions suffer from the disadvantages that they are relatively expensive and the conversion facilities may not be conveniently located close to crop-growing areas.
Attempts have been made in the past to use microorganisms to improve the availability of essential elements in soil systems. For example, known phosphorus-solubilizing bacteria and actinomycetes have been added to soil to increase the levels of available phorphorus. However, such techniques have not found widespread acceptance, perhaps because the micro-organisms were not effective at solubilizing phosphorus in soil or perhaps because their methods of application were difficult or inconvenient.
Accordingly, there is a need for an improved system for increasing the levels of available phosphorus and/or micro-nutrients in soil systems, and particularly in neutral or alkaline soil systems.